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C. J. Potgieter et al.: Pollination in Plectranthus
a d
b
C
I
Pollen loads. Plectranthus pollen grains are
radially symmetrical and 6-colpate with double-
reticulate exine patterns. Pollen grain diameters vary
from 19 x 29 pm (P. ciliatus) and 23 x 24 gm (P.
madagascariensis), to 27 x 37 gm (P. hilliardiae). The
genus is stenopalynous, which makes it difficult to
distinguish between pollen of different species, but it
is possible to distinguish Plectranthus pollen from
grains of other plant species.
Specimens of anthophorid bees and nemestrinid
files that were caught visiting P. ambiguus, P. ecklonii,
m
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f
m
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107
Fig. 6. Six species of Hymenoptera showing
the range in body size and proboscis length
of bees that visit Plectranthus spp. a-d
Anthophoridae: a Amegilla caelestina, b A.
mimadvena, e A. bothai, d A. spilostoma;
e-f Apidae: e Apis mellifera, f Allodape
pemix. Bars: 5 mm
P. ciliatus P. oribiensis and P. madagascariensis were
found to contain more than 90% Plectranthus pollen
on their bodies. In cases where mixed pollen loads
were found the majority of foreign pollen was
restricted to the scopae (of female bees) or dorsally
on the insect body (of flies). Three species of Pieridae
and one of Lycaenidae were the observed butterfly
visitors to P. madagascariensis, but no pollen was
found on these specimens. The pierids were only
abundant towards the end of the main flowering season
(May) in 1996.